Medical imaging techniques, such as computerized axial tomography (CAT) and magnetic resonance image (MRI), now allow medical personal to view three-dimensional images of the organs and tissue within a person. This equipment is used both to diagnose a patient's condition and as an aid in performing surgical procedures. Specifically, it is now possible, to a limited extent, for doctors to perform what is referred to as image guided surgery.
In image guided surgery, an image is initially generated of the body region in which the surgical procedure will be performed. A small transmitter is then placed on the patient. This transmitter is held in place by an appropriate harness or strap to ensure that its position stays constant relative to fixed tissue internal to the patient. Owing to the physical structure of the harness/strap, the position of the transmitter to the fixed tissue points internal to the patient are also known.
Then, the surgical procedure is performed using an instrument to which a complementary sensor is attached. This sensor is a receiver that, based on signals generated by the transmitter, generates output signals representative of its position relative to the transmitter. During surgery, these output signals are forwarded to a processing unit which also maintains data representative of the previously obtained image of the patient's body region. Thus, the processing unit contains data representative of the image of the patient's body, the distance between the transmitter and the patient's fixed tissue points and the distance between the transmitter and the sensor. Using these data, the processor is able to generate data that inferentially identifies where, inside the patient, the instrument is located. This data is then superimposed as a distinct image on an output display on which an image of the patient's body is presented. Thus, the surgeon performing the procedure is able to see where, in the body, the instrument is located even though the surgical site is not directly exposed to the eye.
The development of image guided surgery is making it possible for surgeons to more accurately and easily perform procedures in which the surgical site is concealed or difficult to view. For example, being able to perform image guided surgery is especially useful when performing sinus surgery in which the surgical instruments are inserted into the patient through an existing body opening. Also, being able to precisely identify the location of the surgical instrument can be helpful when performing endoscopic surgery. In this type of surgery, small portals are cut in the patient and elongated instruments are inserted into the portals and positioned at concealed surgical sites. Also, being able to precisely locate surgical tools is important when performing spinal or neurological surgical procedures.
To date, however, the ability to perform image guided surgery is limited. This is because only a few surgical instruments have been designed to work with a key complementary component, the sensor, that makes image guided surgery possible. For example, there have been some probes and aspirators designed to be attached to the sensor. However, it has been very difficult to provide powered surgical tools that can be used to perform image guided surgery. There are several reasons for this. One reason for this is that many powered surgical tools include a handpiece in which there is an electrically driven motor. The magnetic fields that develop when the motor is actuated can interfere with the readings taken by the position-defining sensor.
Moreover, most powered surgical tools are designed to drive a number of different complementary cutting accessories. Common accessories these tools drive include edgers, resectors, shavers, planers and burrs. An advantage of designing a powered surgical tool so that it can be used with these different accessories is that it allows the surgeon, during an operation, to simply change the accessory in order to accomplish a specific surgical procedure. Moreover, by making cutting accessories removable, these accessories can be made disposable. This eliminates the otherwise high costs associated with manufacturing the cutting accessories out of repetitively sterilizable material and the actual expenses associated with sterilizing them. A problem when using these cutting accessories for image guided surgery is that each accessory has unique dimensions. When a cutting accessory is attached to the handpiece, the overall data regarding the dimensions of the surgical tool change. The processor associated with the image generator must take into account this change in the dimensions of the surgical tool in order to ensure that the processor generates data that accurately indicates where, in the patient's body, the tool is located.
To date, it has been difficult to provide a powered surgical tool system that can be used in conjunction with image generating system without affecting the image generating systems sensor and that is configured to ensure that, when the tool's accessory is changed, the image-generating system will continue to properly indicate the location of the tool.